Optimization of Bacillus subtilis Fed-Batch Fermentations for the Maximization of the Synthesis of a Recombinant β-1, 4-Endoglucanase

Abstract

Optimal feed rate profiles in fed-batch fermentations of the system Bacillus subtilis DN1885(pCH7) were calculated for different operational conditions. Optimization was focused on the maximization of the final concentration of a recombinant ß-1,4-endoglucanase synthesized by the recombinant system. Sequential Quadratic Programming was used to derive the optimal feed rate profile which was compared to the optimal constant feed rate. Similar values of enzyme concentration were found with both feeding schemes, they were 4.5-5 % higher with the variable rate. The maximization of the productivity depends on the processing time, the initial culture volume, the inlet substrate concentration and also, to a lesser extent, on the degree of discretization that can be manipulated by means of the feed rate. Dramatic increases in final enzyme concentration were only seen in 2 cases; when the fermentation time was very small (10 h) it increased 43% and when the initial volume in the fermenter was very large (3.75 1) it increased 149%.